The video contrasts pictures of the stylish, British-born Mrs Assad with graphic photos depicting Syria’s conflict and its victims, many of whom are children.

It is accompanied by an open letter which also acts as the script to the video.

It reads: « Stand up for peace, Asma. Speak out now. For the sake of your people. Stop your husband and his supporters. Stop being a bystander. No one cares about your image. We care about your action. »

Escalating violence in Syria has dimmed hopes that the fighting, which the UN says has caused the deaths of more than 9,000 people, could come to an end soon.

Last month Mrs Assad was banned from travelling to the EU. In February she declared she would stand by her husband, in an email sent via an intermediary to The Times.

It read: « The president is the President of Syria, not a faction of Syrians, and the First Lady supports him in that role.

« The First Lady’s very busy agenda is still focused on supporting the various charities she has long been involved with and rural development as well as supporting the President as needed. »

In a statement, Sheila Lyall Grant and Huberta von Voss Wittig said: « We strongly believe in Asma’s responsibility as a woman, as a wife and as a mother. As the vocal female Arab leader that she used to be, as a champion of female equality, she cannot hide behind her husband. »

They added: « Many women in Syria have been victims of the ongoing violence. Many of them have, however, taken the risk of speaking out and standing up for their freedom during the year long demonstrations. We are asking Asma Assad to take a risk too and to say openly: Stop the bloodshed, stop it right now. »

Earlier today Foreign Secretary William Hague criticised Mr Assad’s regime while speaking in the House of Commons.

He told Labour’s Ian Murray (Edinburgh S): « You are quite right to raise doubts about the intentions of the regime, they have complied in the most grudging way possible with the ceasefire and not yet met all of its terms.

« They continued to kill as many people as they could in the opposition until the last possible moment. »